The present invention relates to enclosures for electronic components, and more particularly to enclosures for cathode ray tube assemblies including a video-amplifier printed wiring board located in close proximity to, and structurally separated from the cathode ray tube connector base.
A typical video display monitor or terminal (VDT) 10 as employed with computers, and the like, is shown in simplified form in FIG. 1. The VDT 10 includes a cathode ray tube (CRT) 12 mounted behind a bezel 14 on a horizontal chassis base 16. As necessary and convenient, the chassis base 16 may carry one or more vertical chassis members 18. Typically, a decorative and protective cover is placed around the above-described components.
Connected to the CRT 12 at its electrical connecting point 20 is a video amplifier printed wiring board (PWB). The video amplifier PWB imposes certain requirements relative to its design and positioning. For one, it should be as close as possible to the CRT connecting point 20; that is, the wires between the PWB and the CRT should be as short as possible. For another, provision may have to be made for heat sinking certain high heat-dissipation components on the PWB. For yet another, components emitting radio frequency interference (RFI) and/or electromagnetic interference (EMI) may have to be shielded. In doing all this, the video amplifier PWB and its associated apparatus must not impose possibly damaging forces on the neck 22 of the CRT 12.
One prior art broadly utilized arrangement of locating the video amplifier PWB 24 with respect to the CRT 12 in VDT's such as 10, especially those relatively simple monochrome products with fewer, relatively low heat-dissipation components on the PWB 24, is shown in FIGS. 3 and 4. PWB 24, as an assembly is mounted, via socket 26, directly on the CRT's connector base 28, sometimes with the addition of a mechanical clamp and support 30, acting on the rear of the CRT neck 22. Such a simplified solution involves the transmission of all static and dynamic loads from the PWB 24 directly to the CRT 12, thus making it vulnerable to mechanical damage.
The weight and size of the PWB assembly increases considerably for color VDT's, and further where high heat-dissipation components on board require, for example, finned metal heatsinks for thermal management, and still further where a complete box-like EMI/RFI shield is required around the PWB. The respective weight and size increase makes the arrangement of FIGS. 3 and 4 impractical for CRT mechanical integrity reasons.
To overcome some of those above difficulties, another prior art arrangement, as shown in FIGS. 5 and 6, splits the circuitry, components, and hence the weight, between a chassis-mounted video amplifier PWB 24' proper and an auxiliary CRT board 32 mounted on the connector base 28 of CRT 12 similarly to the arrangement of FIGS. 3 and 4. High heat-dissipation components, requiring a heatsink 38 for thermal management, must be placed on the chassis-mounted PWB 24' to relieve the CRT 12 from mechanical loads. A vented EMI/RFI shield box 34 is also mounted to one of the VDT's chassis members 18 and spaced from the CRT 12 in order to allow for the assembly inaccuracies, dynamic excursions, etc., of the CRT 12 without its coming into mechanical contact with chassis-mounted parts. Special spring-loaded, floating, frictional contacts 36 are used in this arrangement to interconnect the two boards 24', 32, respectively, while limiting mechanical loads transmitted by such interconnect from parts, relatively rigidly mounted to the VDT chassis, to the CRT neck 22. The disadvantages of such an arrangement are its complexity and costliness, the presence of still considerable weight on the CRT base, and multiple thermal interfaces making the thermal path between components requiring heat sinking and the chassis-supported heatsink 38 (via bracket 40) relatively high-resistance.